Orange-Peel-Derived Carbon: Designing Sustainable and High-Performance Supercapacitor Electrodes

Interconnected hollow-structured carbon was successfully prepared from a readily available bio-waste precursor (orange peel) by pyrolysis and chemical activation (using KOH), and demonstrated its potential as a high-performing electrode material for energy storage. The surface area and pore size of carbon were controlled by varying the precursor carbon to KOH mass ratio. The specific surface area significantly increased with the increasing amount of KOH, reaching a specific surface area of 2521 m2/g for a 1:3 mass ratio of precursor carbon/KOH. However, a 1:1 mass ratio of precursor carbon/KOH displayed the optimum charge storage capacitance of 407 F/g, owing to the ideal combination of microand mesopores and a higher degree of graphitization. The capacitive performance varied with the electrolyte employed. The orange-peel-derived electrode in KOH electrolyte displayed the maximum capacitance and optimum rate capability. The orange-peel-derived electrode maintained above 100% capacitance retention during 5000 cyclic tests and identical charge storage over different bending status. The fabricated supercapacitor device delivered high energy density (100.4 μWh/cm2) and power density (6.87 mW/cm2), along with improved performance at elevated temperatures. Our study demonstrates that bio-waste can be easily converted into a high-performance and efficient energy storage device by employing a carefully architected electrode—electrolyte system.